Pulling a Wireless Signal Out of Thin Air
Jul 26, 2012 5:00 AM PT
A cruel fact of life is that mobile operators have a vested interest in building out their networks in areas where there are customers, not where there aren't any. Those towers are expensive, and they want a return.
Unfortunately, that means those of us who enjoy puttering around the vast open spaces that make up most of the United States can't get a signal.
A Femtocell functions by creating a mini-mobile network and then squirting the traffic over a wired broadband connection.
Portable satellite systems are expensive -- often costing more than a dollar a minute for voice. The Femtocells require a fixed location, like your home.
What if you're traveling through remote areas, and want to economically make calls and browse the Web?
The answer is to take advantage of Federal Communications Commission rules that, under certain circumstances, allow you to amplify your phone's power to 3 watts from its designed power level of usually 0.6W.
Step 1: Choose an Amplifier
Select a 3-watt cellular amplifier that meets FCC requirements and will function within the frequencies your network uses. This will be indicated in the marketing collateral and not necessarily on the device itself.
The amplifier must be able to cope with potential cell site overloading. It does this by automatically adjusting amplifier output based on the cell site's signal -- determined by distance to tower and topography. Full power when not needed blows away other users.
Verify that the amplifier has an oscillation protection circuit. Oscillation is like microphone feedback, and if it occurs in amplifiers, it can cause a cell site go offline.
Step 2: Install the Amplifier and Antenna
Connect the phone cradle to the amplifier with the supplied cable. The amplifier kit is supplied with a phone cradle that acts as a low-level repeating antenna; it doesn't need a wired connection to the phone.
Mount the supplied magnetic-mount external antenna to the vehicle's roof by placing it in the center of the roof. The metal roof acts as an important ground plane.
Thread the supplied cable through a door opening. Don't run the cable through a window because it can become damaged, and don't connect the cigarette lighter power until both antennas -- the cradle and external roof antenna -- are connected.
Step 3: Perform a Site Survey
Download a signal strength app like Staircase 3's OpenSignalMaps for Android and touch the "i" button within the app. Apple iPhone users dial *3001#12345#* and then press "Call" to switch the home screen signal bars to dBm.
Read off the dBm with the 3-watt amplifier switched off. This is the unamplified signal strength, and is the power ratio in decibels of the measured power as referenced to 1 milliwatt.
Step 4: Determine the Boostability of Your Signal
A number from the previous step that is closer to zero is better. So, a dBm reading from the previous step, of -71 indicates a better signal than a dBm of -81.
A reading of -120 dBm indicates no signal. You cannot amplify a signal that doesn't exist.
A reading of -110 dBm indicates a marginal signal -- virtually nonexistent, but may be amplified.
A reading of -105 dBm indicates no signal on an iPhone.
Tip: Some phones will not show a reading better than the low 50s, even if signal strength is indeed better.
Move closer to the cell tower if your readings indicate no signal and you know where the tower is; you will improve the signal strength. The OpenSignalMaps for Android app provides tower maps.
Step 5: Perform a Test
Place the phone in the cradle and switch the amplifier on.
Switch the phone's radio to flight mode and back on again. This forces the phone to look for a new signal.
Allow the signal to stabilize for a few seconds, and try the call or data connection.
Is It Worth It?
In my Sprint 3G network tests, I was able to obtain a speed increase of 324 kbps using a 3-watt Wilson Electronics amplifier with 6.12 dBi Wilson Electronics external antenna (Model 811214: US$159.99 at Amazon.com).
The unamplified signal tested at my chosen remote location, with challenging topography, was -85 dBm, and at that signal strength I obtained a 148 kbps download, measured using Ookla's Speedtest.net app.
Amplifying the signal created a -71 dBm signal which gave me a 472 kbps download speed.
At the same location, an unamplified voice call was dropped. I then made the same call with the amplifier switched on and the call was maintained.
Your results will vary based on topography and distance to tower.
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